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A Journal of Applied Mechanics and Mathematics by DrD

## #28 -- Analytical Design -- Part III

Mechanics Corner
A Journal of Applied Mechanics and Mathematics by DrD, # 28
Analytical Design -- Part III      Introduction     In Parts I and II of this series, we began looking into the design analysis for an emergency steam cut-off valve for a nuclear power plant. Part I simply posed the problem, and Part II got into the detailed kinematic analysis of the four bar linkage that is to control the motion of the plug as it shuts off the steam flow. We would like to move on to the dynamic simulation of the motion to get an idea about the time required to close and ultimately to a force analysis so that the links can be appropriately sized. Before that can be done, it is necessary to spend some effort on the design of the plug itself so that the dynamic properties of the plug (mass, mass moment of inertia) can be estimated.
In the stress analysis of the plug, I am at somewhat of a disadvantage with respect to most of you. I know that many of you have access to Finite Element programs which enable you to do a fairly complete and correct stress analysis. Because I am no longer connected with a university or an industry that would give me that access, I have do not have access to FEA. Thus the analysis that I will present here is somewhat crude, rather approximate, and not recommended where better methods are available. You may choose to look at this as somewhat of a "historical approach" to the stress analysis, the way it would have been done before the arrival of FEA. The model that I will present is overly simplified, but it is the best that I can provide for this series.
The maximum temperature and pressure for the steam system are given as P = 1000 psi, T = 1000 deg F or equivalently, P = 68.95 bar, T = 538 deg C. These are the targets specified for the plug design. AnalyticalDesign-Pt3.pdf

## #27 -- Analytical Design -- Part II

Mechanics Corner
A Journal of Applied Mechanics and Mathematics by DrD, # 27
Analytical Design -- Part II      Introduction     In Part I of this series, the problem posed was to apply, as far as possible, the available knowledge of mathematics and science to the design of an Emergency Steam Shut-Off Valve, to be gravity driven as in the sketch below, Fig. 1. The inlet and outlet for the steam flow are both specified to be 0.85 m in diameter, so the valve plug will be a little bit greater than this amount in diameter. That suggest that, as a first approximation, L2 =0.85 m. Now, where do we go from here?

Fig. 1  Proposed Gravity Actuated Emergency Steam Cut-Off Valve.     The draftsman's sketch has been redrawn to scale, and it appears that this is a workable geometry (we will have to investigate that further, but it is a place to start). Scaling his sketch in such a manner that L2 =0.85 m, the first estimate for the dimensions is
L1 = 3.460 m
L2 = 0.85 m
L3 = 0.902 m
L4 = 1.912 m
D = 0.638 m
These are only preliminary, subject to change as needed, but they give us a place to start the kinematic considerations.
There are two issues of major importance to be address early on: 1.Will the plug enter straight into the valve seat without binding or impacting on an edge?
2.How long will it take for the plug to fall into place?     These two issues will be our initial concern.     AnalyticalDesign-Pt2.pdf

## #26 -- Analytical Design -- Part I

Mechanics Corner
A Journal of Applied Mechanics and Mathematics by DrD, # 26
Analytical Design -- Part I      Introduction     On ME Forums, there have been a number of questions raised about design. Many students are writing in asking for ideas for a senior design project, others are asking for help with a design problem, etc. There has been some discussion about "Just what is design?" That was definitely a question in the minds of many faculty at one school where I taught a number of years ago. The engineering accreditation board in the US is called ABET (Accrediting Board for Engineering and Technology), and just before I joined this particular faculty, ABET had denied the school accreditation "because they were not teaching nearly enough design." When the faculty heard that, they were shocked, and we spent several years getting everyone on board with what design is.
I am not going to attempt to launch into a full scale discussion of what constitutes "design," but rather, with this post I am beginning a short series on one narrow aspect of design. Please understand that this is not the full scope of design, but simply a part of it.
In most jurisdictions where engineering is defined legally, the definition will include something like, "being qualified to design," and will also speak of having a sufficient knowledge of mathematics and science to apply those fields to the engineer's work. With this series, I hope to show the application of mathematics and science to a typical design problem. The problem I have chosen is fairly typical of a first cut at a design, but it must not be taken to represent all such problems. The Problem     Suppose that you are a young engineer, working in the nuclear power industry. Because of our natural fear of uncontrolled nuclear energy, one of the constant concerns in the nuclear power industry is how the plant will handle various possible accidents, particular things like an earth quake, bomb strike, or airplane crash onto the nuclear reactor. Any of these events could cause a need to shut down the nuclear steam generation, and bring the whole plant to an orderly halt. We are not about to tackle the entire problem, but just one small part of it, stopping the flow of steam from the system.
In the event of a catastrophic accident, it is not wise to rely on the ordinary control systems that function using electrical actuators, pneumatic systems, or in some cases, hydraulics. All of these energy systems are likely to be disrupted by the emergency, so what is left to actuate a steam valve? AnalyticalDesign-Pt1.pdf

## Professional Societies -- Or Not?

Mechanics Corner
A Journal of Applied Mechanics and Mathematics by DrD
Machinery Dynamics Research, (c)  2016
Professional Societies -- Or Not?
Introduction
This post is written in response to questions raised by one of our regular participants, a young engineer in Australia. What I have to say here is based entirely on my own, very American, experience, and others may have different ideas. I would encourage a general discussion in the comments, so that we may see how various folks look at this question.
The questioner asked, "... have you maintained a membership to such an organization for the purposes of networking and staying active in the engineering world?" I'd like to re-word the question just slightly to read, "What is the purpose for being in a professional society, and is it worth the costs?" My experience in this matter is limited strictly to American professional societies, but I suspect there will be some carry over to other nations as well.
Before getting into the good and bad points, it is worthwhile to cite some examples of various professional societies, so that everyone will understand the kind of organizations are under consideration. Let me name a few that come to mind, just off the top of my head:
ASME --- The American Society of Mechanical Engineers
SAE --- Originally called the Society of Automotive Engineers, now legally simply SAE
ASHRAE --- American Society of Heating, Refrigeration, and Air-conditioning Engineers
NSPE --- National Society of Professional Engineers
ASNE --- American Society of Naval Engineers
SNAME --- Society of Naval Architects and Marine Engineers
AIAA --- American Institute of Aeronautics and Astronautics
IEEE --- Institution of Electrical and Electronic Engineers
SME --- Society of Manufacturing Engineers
ASCE --- American Society of Civil Engineers
AIChE --- American Institute of Chemical Engineers
IIE --- Institute of Industrial Engineers
SAME --- Society of American Military Engineers
SPE --- Society of Petroleum Engineers
AWS --- American Welding Society
This list is certainly not exhaustive; there are many more such organizations. As this brief list suggests, there is an organization for every interest! Let me talk a little bit about a few of these, the ones of which I am a member and one other that I am familiar with.
ASME
In many respects, ASME has long been the premier mechanical engineering society in the US. It first rose to prominence in the early 20th century when there was a nation-wide problem with boiler explosions. ASME took the lead in developing boiler standards, and today the ASME Boiler and Pressure Vessel Code is recognized world wide as a guide to safe design of such systems. Sales of the Code documents are a major source of income for the organization, and ASME is very active in many areas of Codes & Standards. It also published a number of technical journals, such as the Transaction of ASME, Journal of Applied Mechanics. They also organize and host many conferences around the country, and indeed around the world, on various topics of specialist interest.
When I first joined ASME as a student in the early 1960s, it was a very membership oriented organization. Each year, when you paid your dues, you received five coupons that could be redeemed for technical papers that were available from ASME. At that time, the membership really ran the organization. Today, it has all changed. It is simply a business, run by a bunch of folks in New York, for their own benefit, and they simply do not care about the needs of the membership. If I want an ASME paper, I can buy it for about \$25, exactly the same as anyone else can get it. There are ASME Student Sections at most American engineering schools, but ASME does little or nothing to support them. Over the years, I have attended many ASME functions, from local section meetings to national conferences. They are often well attended, and they are an opportunity to meet others in the field.
I am a Life Member of ASME which simply means that I was foolish enough to pay dues for 30 years, and now I am exempt from further dues. I probably would not join ASME if I were starting today with what I know now.
SAE
SAE was originally known as the Society of Automotive Engineers, a fairly self-explanatory name. It has dropped the name to become simply SAE, and refers to itself as "the mobility society." It incorporates folks interested in mechanics, materials, fuels, lubricants, combustion, controls, electronics, etc., and deals with automobiles, trucks, ag machinery, boats, and aircraft. It is very, very broad, and almost any technical person can find a role in SAE. SAE, like ASME, also publishes many Codes and Standards, and organizes a number of technical meetings each year.
One thing that I think is important about SAE is the way it supports engineering education. SAE sponsors, with significant amounts of money, many student design competitions in which undergraduates design, build, and test various real projects. One of the most popular of these is what is called the Mini-Baja Competition, a reference to the famous off-road racing done in Baja California (Lower Califormia, Mexico, a very primitive area located directly south of the US state of Califormia). Let me tell you a bit more about my own involvement with SAE.
In the mid-1980s, I was teaching in a small engineering school in Wisconsin. I was in my office one afternoon when one of my former students burst in, eager to talk to me. Brad said, "Are you a member SAE?" to which I replied, "No, I am a member of ASME." He came back with "Well, would you be?" which really puzzled me. Why did he care whether I would join SAE or not? As the whole story came out, he was nearing graduation, and he wanted to do something of lasting value for the school. His idea was to organize a SAE Student Chapter and get them involved with the Mini-Baja race car competition. Such a group would need a faculty adviser, and he wanted me to be that adviser. To make a long story short, I joined SAE and we got approval to organize a Student Chapter and got started on the construction of a race car. I was amazed at the student enthusiasm, and also at the financial support we got from the Senior Section (the adult SAE Section in our area). Money poured in from the Senior Section, and we received a donated engine (everyone uses the same engine) and many items of donated hardware. We did not win that first year, but we did the next year, and I'm proud to say, the group continues to this day, doing very well year after year! A couple of years ago, I attended an SAE student competition where they were racing Formula I race cars. We had about 25 schools represented, coming from as far as 1000 miles away for the competition! This is a serious boost for engineering education, and a real service!
SNAME
SNAME is the place where most naval engineering is focused. They publish a high quality series of technical journals, and deal with real marine engineering, including ships, off-shore platforms, ice-related problems, etc. I joined primarily because they are the only ones who seem to be concerned with a particular vibration problem that interests me. I have not solved that problem yet, but when I do, I'm sure I will publish the results in a SNAME journal. ASNE
For contrast with SNAME, there is the American Society of Naval Engineers. I became aware of this organization when I worked for the US Navy, and found that it is mostly Navy officers, government big-shots, government contractors, and others, all pretending to be engineers. Their meetings (I went to several) are about as technical as a comic book. The only reason to be a member here is for the contacts one might make; the technical content is just about nil.
Summary
So, back to the main question: Is it worth it?
That depend entirely on your own goals and values. Are you interested in it for a social outlet? Are you interested in terms of community service? Are you hoping it may provide you a contact that could lead to a better job? Are you hoping to learn serious new engineering content? Before I would commit to one of these organization, I would try to investigate just how it fits into your own hopes.
Most such organizations welcome visitors to your meetings, so you can probably visit a time or two and get some feel for the organization at your local level. Ask what does it do? What projects has it undertaken? Ask yourself if the meeting is well run and organized (I'd stay clear of disorganized groups; they are simply too boring for words!) Ask how often they meet, and what they do in their meetings. I have been on some really excellent field trips as part of various society meetings, and I have often taken students with me to these meeting where there was a field trip involved. I have also been to some really terrible meetings, with a dinner of rubberized chicken and a meandering, dull-as-dust speaker. They vary all over the map.
I would suggest that every engineer should probably be a part of some such organization, but that should be chosen with real care. Check out prospects very carefully, find out what you might expect to get out of it, what you might expect to contribute, and what the financial cost is. Their can be real benefits, but not every possible choice leads to them. Make a wise choice!

DrD is a retired Professor of Mechanical Engineering in the USA. He can be reached for comments, questions, or requests through the ME Forum message system.. Be sure to check back soon at www.http://mechanical-engineering.in/forum/blog/206-mechanics-corner/ for more articles.

## War Stories

Mechanics Corner
A Journal of Applied Mechanics and Mathematics by DrD

## #25 -- A Textbook Statics Problem

Mechanics Corner
A Journal of Applied Mechanics and Mathematics by DrD, # 25
A Textbook Statics Problem      Introduction     In the course of each day, I visit many web sites, always keeping an eye out for interesting engineering problems. The problem that is discussed here is one such that came from an American site (more about that web site later). The problem was presented as a simple statics problem, and the poster was asking for help in the solution. There were several replies with suggestions, but no one seemed to be able to really put their finger on the difficulty. As it turns out, this problem presents multiple difficulties, and offers an opportunity to look at several matters of interest to this readership.
The question was posed with a hand drawing comparable to that shown in Fig. 1 here.

Fig. 1  Schematic Drawing as Given     The person posting this problem implied, without ever clearly stating it, that the problem is to find Fex when the applied load T=100 N as indicated. He says, "So it's been a while since I've done FBDs, and what seems like a simple problem is causing me grief. ... Can someone tell me what I've done wrong here? I seriously was looking at this all day and was just scratching my head." Can any readers relate to the dilemma of this poster?
Just looking at the sketch, it seems like a reasonable problem. When the load T is applied, it will tend to rotate the crank ABC in a clockwise direction, straightening the joint at C. This will push the roller at E against the wall, developing the reaction force Fex. There is no friction at either D or E, so what is the difficulty? TextbokStaticsProb.pdf

## Torsional Stiffness of a Shaft - Part III -- #24

Mechanics Corner
A Journal of Applied Mechanics and Mathematics by DrD, # 24
Torsional Stiffness of a Shaft -- Part III
Introduction
The discussion in previous parts of this series has focused on stiffness (or compliance) estimates for various shaft geometries. There has been nothing said yet about joining parts together, although most readers will readily agree that integral (single piece) shaft assemblies are very rare in practice. It is time to discuss joining multiple components together to form a shaft system.
The list of possible coupling types is almost endless, so this article will simply focus on a few of the more common types to illustrate the thought processes. Keyway or Spline     Before considering actually joining to a second member, if the connection is to be made by means of a key or a spline, it is appropriate to look at the way in which the keyway (or spline) itself increases compliance in the section where there is no torque transfer.

[Fig. 1  Shaft Sections with Keyway (left) and Spine (right)]     Where a key is used, the keyway is usually cut significantly longer than the key itself. This results in a section of the shaft that effectively has reduced diameter. Experience has shown that this can be treated adequately by considering it to be a uniform solid shaft of diameter Deff as shown in Fig. 1.
Similarly, where a spline is used, it is not difficult to see that the ribs that form the spline teeth carry no significant shear. Thus the part of the shaft that is splined is also properly modeled as a uniform solid shaft with diameter Deff as shown in Fig. 1. ShaftStiff-Pt3.pdf

## Torsional Stiffness of a Shaft - Part II -- #23

Mechanics Corner
A Journal of Applied Mechanics and Mathematics by DrD, # 23
Torsional Stiffness of a Shaft -- Part II
Introduction

In the previous post of this series, a variety of shaft forms involving both solid and hollow sections were considered. A general approach was developed, applicable to various sorts of non-uniform shafts, but always subject to the provision that the variation in section was gradual; no sudden changes in section were permitted among the forms considered. This leads directly to the question that is the focus of this post: "How are sudden changes in diameter taken into account?" Steps, also called "shoulders" are a common feature of many shaft designs, used to locate rotating elements (fans, flywheels, pulleys, etc) on the shaft. They are also used in connection with bearings and seals. It is important that the means be established to account for shoulders in the shaft stiffness calculations.
Compliance of a Stepped Shaft     At typical shaft section involving a step or shoulder is shown in Fig. 1. As usual, it is assumed that all of the dimensional data is known. The difficulty is the rather abrupt step from diameter D1  up to D2 . For the development below, it is always understood that D1 < D2. By the methods previously established in Part I, the compliance of each shaft segment can easily be computed,
ShaftStiff-Pt2.pdf

## Torsional Stiffness of a Shaft -- Part I -- #22

Mechanics Corner
A Journal of Applied Mechanics and Mathematics by DrD, # 22
(c)  Machinery Dynamics Research, 2016
Torsional Stiffness of a Shaft -- Part I

Introduction

A shaft is a common machine element, used to transmit rotational motion and torque from one component to the next. It is clear that the length of the shaft must be sufficient to span the distance from the first component to the second, but what should the diameter be? The answer to this question requires first answering two related questions:
-->  How much torque is to be transmitted? This will define the strength requirements for the shaft so that it does not fail under load.
-->  What stiffness is required for the shaft? This will determine the angular relation between the two ends of the shaft, important in cases where angular displacement accuracy is a concern and also a major factor in the torsional vibrations of the system.
As is typical with a design problem, the designer is not able to simply specify what is required and compute the required dimensions. Rather, it is necessary to propose a design, that is, to propose both shape and dimensions, and then see if the strength and stiffness requirements are met by the proposed design. There are many possible designs for a shaft, so it is important to deal with the necessary stiffness calculations for a variety of geometries (the matter of strength is left to another time).
The basic theory required for this work is commonly found in all Mechanics of Materials textbooks (see for example, Timoshenko). There are also two well known references that deal specifically with this material. The first is the BICERA Handbook (which is the source for many of the ideas in this note) and also the work of Wilson. TorsionalStiffnessOfAShaft.pdf

## Professional Responsibility — Do The Right Thing

1. Perhaps the most obvious is computer graphic trickery, where the video has been manipulated to show something that never really happened.
2. Perhaps there is a hidden motor, driving the system through concealed belts and/or gears. This would have to be done with considerable skill, but it is certainly possible.
3. One of the most interesting possibilities is that of manipulation of powerful magnets below the table. This last is interesting from a technological standpoint. Permanent magnets have been known to man for a very long time, but really powerful permanent magnets are a relatively recent improvement. This has been brought about the application of various rare earth elements such as Samarium-Cobalt. Today, using rare earths, we have permanent magnets far more powerful than the permanent magnets of previous generations, and many people have looked in this direction for a “new” energy source. I think such a search is misguided, but I cannot say that it is impossible. But if it is necessary to move the permanent magnets, that movement constitutes a work input to the system, and must be taken properly into account. So, where does professional responsibility come into the ME Forum discussion? As engineers, we have the duty, the obligation, to call out false demonstrations wherever they are shown. If we fail to do this, we are tacitly endorsing the false representations. We do not want to be put in the position of having someone invest in ignorance in such schemes, thinking that we approve of them. We have a responsibility to speak out against falsehood wherever it is found. For this reason, I urge every reader of ME Forums to review the material presented by these two frauds and then to protest to the site owner by an internal e-mail (saurabhjain Administrator). These sites should be urged first to make a correct, honest presentation of their ideas. If that is not done, they should be removed from ME Forums. It is time for all Forum readers to speak up! We have to do the right thing!

## #21 -- Rigid Body Rotordynamic Instability, Part I

Mechanics Corner
A Journal of Applied Mechanics and Mathematics by DrD, #21
Rigid Body Rotordynamic
Instability, Part I      Introduction     The rotating elements of machinery are usually balanced to avoid vibration which results in noise and fatigue damage. That said, perfect balance is not possible, and there are practical and economic limits to the effort that can be expended to balance machine components. Consequently, every rotating element has some degree of unbalance. This is usually slight, but it is always present.
As rotating elements increase in speed, the forces arising from unbalance increase as the square of the speed. At very low speeds, this usually causes no problem at all, but at higher speed, the increased deviation of the rotating element will eventually cause a collision or a rub. If this is allowed to persist for any length of time, it will often mean a wreck on the machine, with major damage to the rotor and the support structure. This is considered a loss of stability because the operating state deviates ever more and more with increasing speed. Interestingly, in many cases, if it is possible to get through the critical speed (the speed at which maximum deviation occurs), it is often possible to reach lower levels of deviation at higher speeds.
Because rotating elements are so very common in continuously operating machinery, the whole area of rotor dynamics has become extremely important and major efforts are made to understand the phenomena. The applications range from simple motor driven machinery to jet engines. Steam and gas turbines are included as well as all turbo pumps and compressors, so it is evident that this is a very broad topic. One of the most famous rotor dynamic stability problems involved the turbo pump on the space shuttle main engine. This problem was solved by my friend, Prof. Dara Childs. Here we consider only an elementary example as an introduction to a very broad and complex field.
For this short introductory article, consider the system shown in the upper part of Fig. 1, a rigid rotor enclosed in a rigid housing. The entire assembly is mounted to the wall at left with a spring and damper assembly. The center of mass of the rotor is off the axis by an amount ε. As drawn, ε appears quite large, but in actual practice it will be some tiny amount, typically less than one millimeter. The rotor remains centered in the housing at all times, and rotates at a constant angular speed Ω rad/sec. The horizontal displacement of the rotor axis is x(t), where x=0 is the stress free state of the spring.   RigidBodyRotorDyn-Part1.pdf

## #20 -- A Question of Stability (Revised)

Mechanics Corner
A Journal of Applied Mechanics and Mathematics by DrD, #20
A Question of Stability Introduction     The word stability in its several forms is widely used in nontechnical communication. A person whose life it highly consistent from day to day is said to have a stable life. When the political situation in a particular area appears to be unlikely to change, it is said to be stable. A person who is well balanced and unlikely to be easily provoked to anger is said to be a stable person. When the medical condition of a sick or injured person ceases to get worse, the person is said to be stabilized. A company on the verge of bankruptcy is said to be an unstable company. But what does the word stability mean in a technical context? Each of the foregoing examples hints at the technical meaning without really being explicit about it.   A factor g = accel of gravity was missing in the potential energy expression. That is now corrected.

Stability.pdf

## Value Engineering

A toothpaste factory had a problem.  They sometimes shipped empty boxes, boxes without the tube inside. This challenged their perceived quality with the buyers and distributors. Understanding how important the relationship with them was, the CEO of the company assembled his top people. They decided to hire an external engineering company to solve their empty boxes problem. The project followed the usual process: budget and project sponsor allocated, RFP, and third-parties selected.  Six months (and \$8 million) later they had a fantastic solution - on time, on budget, and high quality.  Everyone in the project was pleased.  They solved the problem by using a high-tech precision scale that would sound a bell and flash lights whenever a toothpaste box weighed less than it should. The line would stop, someone would walk over, remove the defective box, and then press another button to re-start the line. As a result of the new package monitoring process, no empty boxes were being shipped out of the factory. With no more customer complaints, the CEO felt the \$8 million was well spent. He then reviewed the line statistics report and discovered the number of empty boxes picked up by the scale in the first week was consistent with projections, however, the next three weeks were zero! The estimated rate should have been at least a dozen boxes a day. He had the engineers check the equipment, they verified the report as accurate.  Puzzled, the CEO traveled down to the factory, viewed the part of the line where the precision scale was installed, and observed just ahead of the new \$8 million dollar solution sat a \$20 desk fan blowing the empty boxes off the belt and into a bin.  He asked the line supervisor what that was about.  "Oh, that," the supervisor replied, "Bert, the kid from maintenance, put it there because he was tired of walking over, removing the box and re-starting the line every time the bell rang.”

## Flying Fun

The URL below will take you to some amazing pictures and a story about the SR-71 aircraft. In my own opinion, this aircraft is some of the most stunning engineering ever done on earth. Enjoy the pictures and the story! DrD http://www.tickld.com/x/jaw/military-pilot-shares-the-most-amazing-story-ever

## How to Ask for Help

If I suggest a project in IC engine design to a student whose interest is mostly in wind power, it is most likely a wasted effort on my part. Why should I spend the time on something to no point at all? It does not help the student because he will not likely use the idea, and I really don’t like having my time wasted. Nature of the Project
Is this project supposed to be a research project (design and execute an experiment to study something), or a design project (design a new gadget), or a design, build, and test project? There is a wide range of project types, and there is no point at all in getting a detailed suggestion for a project of the wrong type. Again, it wastes my time and does not help you. Scope of the Project
Is this project supposed to be a purely pencil and paper project (nothing built, no computer work), or something more? Is it expected to include a computer simulation or FEA stress analysis? Is it expected to include a build and test phase? How much time is expected to be put into this project? A man-week, a man-month, or more? These are vastly different project scope levels, and there is no point to receiving a suggestion for a project that is too much or too little in scope. Resources

## The VEProject --- Shifted Levers --- A Critical Assessment

The VEProject --- Shifted Levers
The video shows a "Shifted Lever" mechanism, a device that appears to be perpetually off balance. It is presented as a perpetual motion mechanism, that is, a machine that will run forever without any energy input other than, perhaps, an initial push. This presentation comes from the VEProject, where VEProject stands for "Visual Education Project." An educational project can be presumed to be a presentation of truth, so should we accept that the author believes that this device is truly a perpetual motion device, or that he is attempting to deceive the viewer?
As most Mechanical Engineers know, the laws of thermodynamics show that there cannot be perpetual motion. So, are the laws of thermodynamics incorrect, or are we being deceived? VEP-ShiftedLevers-Article.pdf

## Twenty One Rules for Tech Writing

Following these rules does not assure that your paper will be accepted by one of the leading journals of the world, but failure to follow them virtually assures that your paper will fail. The whole idea of writing a paper is to communicate something to a reader, and these rules are largely about steps that you, the author, can take to facilitate that communication. If what you say is not interesting or is unclear, then there will be no communication. These rules are all about clarity and ease of communication.

## What/Where to Study -- Another Opinion Piece

What/Where to Study Introduction I do not have the definite statistics available, but it appears to me that the majority of the readership of ME Forums is made up of students, with a much smaller number of readers at other points in their careers. By far the greatest part of these students appear to be in India, with a number in Southeast Asia and the Middle East; there are of course a few folks scattered all over the globe. It has been very interesting to me to learn about all of you, to gain an insight into your interests and concerns. I have been very surprised by a few of the things I've learned. There are two themes that stand out in my mind:
(1) there is much uncertainty about what to study, that is, what to choose for a major,
and
(2) where to study.

## Help!! -- I'm Looking For A Book -- Update!

For quite some time now, I have been looking for a book that just does not seem to exist anymore. The title and author are -- Title:          Secondary Resonance and Subharmonics in Torsional Vibrations
Author:      Per Draminsky It was published in Denmark, around 1961, or so I am told. It seems that it was probably a monograph, a single extended article that filled an entire volume of a journal. If anyone know where this can be found, I would much appreciate help with it. If I can borrow it from a source, that would be wonderful. If it cannot be borrowed, can I pay to have it scanned in and sent to me as a PDF? Is there yet some other way? I am hoping that, with the world-wide readership of ME Forums, someone will help me find this book. If you have some information, please send me an e-mail at DrD@machinerydynamicsresearch.com Thanks for your help. DrD   Many thanks to Sunil Baily who pointed me in the correct direction. I now have, on my desk in front of me, the only library copy of this paper to be found in the Western Hemisphere. It was a bit of a struggle, but I finally got an Inter-Library Loan (ILL) through my local city library. This is going to be very interesting reading (I've already skimmed through it once lightly).

## #19 -- Vibrations - Part VI / Machinery Torsional Vibrations

Mechanics Corner
A Journal of Applied Mechanics and Mathematics by DrD, # 19
Vibrations -- Part VI
Machinery Torsional Vibrations      Introduction     The preceding five parts of this series on vibrations have dealt with relatively simple system, even though those systems are representative of many real situations encountered in engineering practice. For this section, a very specific class of machinery vibration problems, the torsional vibration of engine-driven machine trains involving multiple degrees of freedom, is considered in more detail.
The system considered here is one from the writer's own engineering experience, a small diesel powered generator set. The engine is a Detroit Diesel 2-71 engine driving a Lima Electric 20 KW generator to create 60 Hz AC power for a portable field electrical source. The system for torsional vibration analysis is shown schematically in Fig. 1. VibsVI-MachineryTorsionalVibs-3.pdf

## #18 -- Free-Free MDOF Vibrations / Part V

Mechanics Corner
A Journal of Applied Mechanics and Mathematics by DrD, # 18
Vibrations -- Part V
Free-Free Systems Introduction     In the first three parts of this series on vibrations, only single degree of freedom systems were considered. In Part IV of the series, the idea of multiple degrees of freedom vibrations was introduced particularly in the context of two degree of freedom systems. In this, the penultimate part of this series, another aspect of multidegree of freedom systems is introduced. This is particularly relevant to machinery vibration problems.

Figure 1  Free-Free Translating System
Consider the system shown in Figure 1. At first glance, it is very similar to the system considered in Part IV, but notice that there is only one spring here. The really critical distinction is that there is no part of the system that is stationary, nothing is anchored. Since both ends are free to move, it is called a Free-Free System. VibsIV-Free-Free-Sys.pdf

## Something Light -- A few jokes

1. Team building is very popular in industry these days, so here is a team building joke. A group of mathematicians are attending a weekend seminar on team building. During the night, a fire breaks out in the room of one of the mathematicians. He quickly tears pages out of his notes and lights them on fire, one by one. He then runs down the hall, shoving burning sheets of paper under the doors of all the other mathematicians. In the morning, after the building is burnt to the ground, the fire marshal asks how the fire spread so fast. The initiator spoke up and said, "I thought distributing the problem would lead to a quicker solution." 2. Summary of the important laws that MEs must know: From statics,  Stuff does not move on its own. From dynamics: Stuff fights back (Newton's 3rd Law) From mechanics of materials: Stuff stretches and breaks (Hooke's Law) 1st Law of Thermo: You can't win. 2nd Law of Thermo: You can't break even. 3rd Law of Thermo: You can't stop playing. Addendum: Entropy isn't what it used to be. 3. An engineer, a physicist, and a statistician go hunting together. When some game is sighted, the physicist calculates his trajectory using ballistic equations, but omits air resistance. His shot falls 5 meters short. The engineer adds a fudge factor to compensate for air resistance, but his shot fall 5 meters long. The statistician shouts, "We got 'em!" 4. An engineer and a physicist are lost in a hot air balloon drifting along. The physicist is busy trying to use sextant to determine their position when the engineer spots someone on the ground. The engineer yells, "Where are we?" The man on the ground calls back, "You are in a hot air balloon, 100 ft above ground." The engineer and the physicist look at each other and one says, "That man is a mathematician. His answer was entirely correct and completely useless." 5. There is a calculus party and all the functions have been invited. ln(x) is talking with some trig functions when he see his friend e^x sulking in a corner. He says, "What's wrong, e^x?" e^x replies, "I'm lonely," to which ln(x) replies, "You should try to integrate yourself into the crowd." In despair, e^x cries out, "It won't make any difference at all!" 6. If you can just remember all these jokes, you will be a hit at the next of those parties you imagine yourself being invited to.

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